Net Energy Value for Lactation of High- and Low-Protein Diets Containing Corn Silage

Abstract

Fifty-two complete energy balance trials were performed with lactating and dry cows consuming 40% of the dry matter from concentrate and 60% from corn silage. Two concentrate mixtures were given so that the total diets contained 16.0 and 11.2% crude protein. The diets were fed in amounts near calculated requirements to prevent changes in body tissue reserves. Total energy balance was measured by complete collection of feces, urine, and milk during a 10-day metabolism trial and by measurement of heat and methane production by open-circuit indirect calorimetry during four consecutive 24-hour periods within the metabolism trial. Regression of total energy balance on dry matter intake indicated net energies of 1.55 and 1.45 Mcal NEmilk/kg dry matter for the high and low protein diets. The lower net energy of the low protein diet was explained by a decreased digestibility of energy rather than reduced metabolic efficiency.